An example of an implantable pressure sensing device is disclosed in U.S. Pat. No. 4,846,191 to Brockway et al. Such an implantable pressure sensing device utilizes a sensor assembly including a pressure sensor and a fluid-filled catheter. The fluid-filled catheter refers pressure from a measurement site to the pressure sensor which converts the pressure signal into an electrical signal.
With a chronically implantable pressure sensing device such as that described in Brockway et al. '191, the stability of the device is preferably high, thus reducing the adverse effects of drift that lead to measurement inaccuracies over time. For example, the pressure sensor in a commercially available pressure measurement device designed to be implanted in mice (Data Sciences International Model No. PAC-20) has a specified maximum drift rate of 2.0 mmHg per month, and has been observed to have an average drift rate of 0.75 mmHg per month, with a best known drift rate of 0.25 mmHg per month. For some applications, such as chronically implanted human devices, it is desirable to have even lower drift rates.